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The NN-Explore Exoplanet Stellar Speckle Imager, or NESSI, utilizes two electron-multiplying CCD cameras to simultaneously capture speckle images in two channels split by a dichroic at 686.4nm. Speckle observations provide resolutions at or near the diffraction limit of the telescope, allowing detection of faint companions to target stars with relative astrometry and photometric characterization with a contrast level of approximately 5 magnitudes.
NESSI is primarily operated in queue mode at WIYN where it is most frequently utilized by NN-Explore observing programs. Targets include known or candidate exoplanet host stars that are scrutinized for secondary or other nearby sources and other stellar samples of interest to the exoplanet or stellar astronomy communities. NESSI also has unique capabilities for doing high speed photometry or other observations that can utilize its unusual plate scales.
NESSI's EMCCDs can operate with high sensitivity and low readnoise, even at very fast readout rates. The maximum frame rate for imaging over the full 1024x1024 pixel detectors with no binning is 26fps (38ms exposures). By using subwindows and binning, the cameras can operate at higher frame rates.
For diffraction-limited speckle imaging, NESSI operates with a 19x19 arcsec field of view and 0.018 arcsec/pixel plate scale. NESSI can also switch on the fly to its "wide-field" mode which expands the field of view beyond 70 arcseconds. Each 6-slot filter wheel comes with two ~40nm wide speckle filters. SDSS ugriz filter occupy other slots.
Further information on NESSI can be found on these web pages.
Wide Field Mode Speckle Mode Telescope Focal Plane: Telescope f/#: 6.289 6.289 Plate Scale: 9.374 arcsec/mm 9.374 arsec/mm Focal Lengths: L1 Focal Length: 100mm 30mm L2 Focal Length: 150mm 200mm Optical Path: Tel. Focus: 0mm = 0in 0mm = 0in L1: 100mm = 3.937in 30mm = 1.181in L2: 258.4mm = 10.173in 278.4mm = 10.961in Detector: 150mm = 5.906 200mm = 7.874in Total Length: 508.4mm = 20.016in 508.4mm = 20.016in Detector Image Plane: Magnification from Tel. focal plane: 1.5x 6.67x Pixel Scale (13 micron pixels): 0.0813 arsec/pix 0.0182 arsec/pix Unvignetted Circle Dia.: 56 arcsec 22 arcsec Square Detector FOV: 83 x 83 arcsec 19 x 19 arcsec
1024 x 1024 pixel electron multiplying CCDs (Andor Ixon Ultra 888's). The electron multiplying aspect of EMCCs allows imaging at higher speeds than traditional CCDs because the readnoise is effectively lowered. High speeds are also made possible through shutterless operation in a frame transfer mode.
Filter Wheel A Centeral λ, bandwidth Filter Wheel B Central λ, bandwidth SDSS/u 354.3nm, 32.7nm SDSS/i 765.4nm, 146.4nm SDSS/g 480nm, 151.1nm SDSS/z 943.3nm, 242.7nm SDSS/r 620nm, 143.5nm 716 716nm, 51.5nm 467 467.1nm, 44nm 832 832nm, 40.4nm 562 562.3nm, 43.6nm
NESSI Field Of View
Last modified: 17-Feb-2022 12:58:17 MST
- Observing at WIYN